Method for controlling an electronic circuit

ABSTRACT

A method for controlling an electronic circuit by means of the first, second and third operating parameters, comprises: determining a range of variation of the third parameter for each value of the first parameter by varying the second parameter, said ranges being different; determining a target value of the third parameter; if the target value is within one of the ranges, operating the electronic circuit by setting the third parameter to the target value; and in the opposite case, selecting the two ranges framing the target value and operating the electronic circuit by consecutively bringing the third parameter into each one of the selected ranges.

The present patent application claims the priority benefit of Frenchpatent application FR13/58541 which is herein incorporated by reference.

BACKGROUND

The present application relates to an electronic circuit control methodand to an electronic circuit control system.

DISCUSSION OF THE RELATED ART

There exist methods enabling to decrease the electric power consumed byan electronic circuit while keeping the operating performances desiredfor the electronic circuit. Such methods generally comprise modifying anoperating parameter of the electronic circuit, for example, theelectronic circuit power supply voltage and/or the clock frequency atwhich the electronic circuit is rated.

When two operating parameters of the electronic circuit aresimultaneously modified to decrease the electric power consumed by theelectronic circuit, there exist control methods enabling to determinethe values of these parameters for which the consumed power is thelowest possible while achieving the desired operating performances.

The publication entitled “Energy optimal speed control of devices withdiscrete speed sets” of R. Rao and S. Vrudlhala (Design AutomationConference, 2005, Proceedings—42nd, pp. 901-904, Jun. 13-17, 2005)describes an example of such a control method.

To further decrease the power consumed by the electronic circuit, it isdesirable to further modify a third operating parameter of theelectronic circuit. An example of a third operating parameter is thebulk bias voltage of metal-oxide field effect transistors, also calledMOS transistors, of the electronic circuit.

However, known control methods are not capable of controlling more thantwo operating parameters of the electronic circuit to decrease theelectric power consumed by the electronic circuit while obtaining thedesired operating performances. In particular, such control methodsgenerally do not enable to ascertain that the consumed power whichresults from the determined values of the three operating parameters issubstantially the lowest possible.

SUMMARY

Thus, an object of an embodiment is to at least partly overcome thedisadvantages of previously-described control methods.

Another object of an embodiment is for the control method to ascertainthat the power consumed by the electronic circuit is substantially thelowest possible.

Another object of an embodiment is for the control method to operate inreal time.

Thus, an embodiment provides a method of controlling an electroniccircuit with first, second, and third operating parameters, comprisingthe steps of:

-   -   (a) determining a variation range of the third parameter for        each value of the first parameter by varying the second        parameter, said ranges being different;    -   (b) determining a target value of the third parameter;    -   (c) if the target value is located in one of the ranges, having        the electronic circuit operate by taking the third parameter to        the target value; and    -   (d) in the opposite case, selecting the two ranges closest to        the target value on either side thereof and having the        electronic circuit operate by successively taking the third        parameter into each of the two selected ranges.

According to an embodiment, the first parameter takes first discretevalues, the second and third parameters continuously varying, each pairof one of the first values of the first parameter and of a second valueof the second parameter having an associated third value of the thirdparameter.

According to an embodiment, the method comprises the steps of:

-   -   determining the curve of variation of data representative of the        power or of the energy consumed by the electronic circuit        according to the third parameter, by varying the second        parameter for each first value of the first parameter;    -   determining the convex or concave envelope of the curve; and    -   extracting said ranges from the envelope.

According to an embodiment, the target value is determined for theexecution of a task by the electronic circuit within a given timeperiod.

According to an embodiment, at step (c), the first parameter is taken tothe first value corresponding to the range containing the target valueand the second parameter is taken to the second value of the pairassociated with the target value.

According to an embodiment, the method comprises, at step (d),determining at least one fourth value of the third parameter containedin one of the ranges and smaller than the target value and determining afifth value of the third parameter contained in one of the ranges andgreater than the target value, and the operation of the electroniccircuit for a first time period by taking the third parameter to saidfourth value, by taking the first parameter to the first valuecorresponding to the range containing the fourth value and by taking thesecond parameter to the second value of the pair associated with thefourth value and the operation of the electronic circuit for a secondtime period by taking the third parameter to said fifth value, by takingthe first parameter to the first value corresponding to the rangecontaining the fifth value and by taking the second parameter to thesecond value of the pair associated with the fifth value.

According to an embodiment, the first parameter is the power supplyvoltage of the electronic circuit.

According to an embodiment, the second parameter is the bias voltage ofmetal-oxide field effect transistors of the electronic circuit.

According to an embodiment, the third parameter is the clock frequencyat which the electronic circuit is rated.

According to an embodiment, the method is implemented for the control ofa plurality of electronic circuits, comprising the steps of:

-   -   if the target value is located in one of the ranges of one of        the electronic circuits, having said electronic circuit operate        by taking the third parameter to the target value; and    -   in the opposite case, selecting one of the electronic circuits        and, for said electronic circuit, selecting the two ranges        closest to the target value on either side thereof and having        said electronic circuit operate by successively taking the third        parameter into each of the two selected ranges.

According to an embodiment, the electronic circuit comprises at leasttwo electronic circuit sections, a rank being assigned to eachelectronic circuit section, and the first parameter is said rank.

Another embodiment provides a system of control of an electronic circuitwith first, second, and third operating parameters, the electroniccircuit comprising a first unit capable of determining a range ofvariation of the third parameter for each value of the first parameterby varying the second parameter, said ranges being different, the systemcomprising a second unit capable of determining a target value of thethird parameter, the electronic circuit comprising a third unit capableof taking the third parameter to the target value if the target value islocated in one of the ranges and, in the opposite case, selecting thetwo ranges closest to the target value on either side thereof andsuccessively taking the third parameter into each of the two selectedranges.

Another embodiment provides a method of analyzing an electronic circuitenabling to determine optimal operating configurations of the electroniccircuit according to a given performance criterion, each operatingconfiguration of the electronic circuit being defined by values taken byfirst, second, and third operating parameters, the first parametersbeing capable of taking first discrete values, the second and thirdparameters being capable of continuously or discretely varying, thesecond parameter being capable of varying between a minimum value and amaximum value, each pair of a first value of the first parameter and ofa second value of the second parameter having an associated thirdlimiting value of the third parameter beyond which the circuit is likelyto longer operate, the method comprising the steps of:

-   -   a) determining, for each value of the first parameter, a        limiting variation range of the third parameter by varying the        second parameter between the minimum and maximum values of this        second parameter and by searching the third corresponding        limiting values of the third parameter; and    -   b) determining, for each value of the first parameter, an        optimal variation range of the third parameter corresponding to        all or part of said limiting variation range of the third        parameter previously determined for the value of the first        considered parameter, so that the optimal variation ranges        retained for the different values of the first parameter are all        different.

According to an embodiment, the method further comprises an additionalstep c) between steps a) and b), step c) comprising determining a curveof variation of data representative of said performance criterionaccording to the third parameter, by defining, for each first value ofthe first parameter, an arc of a curve corresponding to the values ofsaid representative data obtained over the limiting variation range ofthe third parameter associated with the first considered parameter andthe corresponding variation range of the second parameter and, at stepb), for each value of the first parameter, an optimal variation range ofthe third parameter corresponding to all or part of said limitingvariation range of the third parameter previously determined for thevalue of the first considered parameter is determined, so that theoptimal variation ranges retained for the different values of the firstparameter are all different and so that the portions of arc of a curveassociated with the retained optimal variation ranges meet at best theperformance criterion of the electronic circuit for the correspondingvalues of the third parameter.

According to an embodiment, step c) comprises the steps of:

-   -   determining the convex or concave envelope of said variation        curve (C); and    -   searching for the portions of said limiting variation ranges of        the third parameter which correspond to said envelope and        retaining these portions as optimal variation ranges.

Another embodiment provides an electronic circuit control methodenabling to determine an optimal operating configuration of theelectronic circuit according to a given performance criterion, eachoperating configuration of the electronic circuit being defined by givenvalues of first, second, and third operating parameters, the firstparameter being capable of taking first discrete values, the second andthird parameters being capable of varying continuously or discretely,the electronic circuit comprising means for storing informationpreviously obtained by the analysis method such as previously definedand comprising, for each value of the first parameter, an optimalvariation range of the third parameter associated with a correspondingrange of values of the second parameter, the optimal variation rangesall being different, the electronic circuit comprising analysis meansenabling, for each pair of one of the first values of the firstparameter and of a second value of the second parameter, to associatetherewith a third value of the third parameter, the method comprisingthe steps of:

-   -   d) determining a target value of the third parameter;    -   e) if the target value is located in one of the optimal        variation ranges of the third parameter, selecting this optimal        variation range and having the electronic circuit operate by        taking the third parameter to the target value; and    -   f) in the opposite case, selecting the two optimal variation        ranges of the third parameter closest to the target value on        either side thereof and having the electronic circuit operate by        successively taking the third parameter into each of the two        selected optimal variation ranges, between a lower value and an        upper value of the third parameter on each side of the target        value; and        at steps e) or f), the first parameter is taken to the first        value corresponding to the range containing the third applied        value and the second parameter is taken to the second value of        the pair associated with the third applied value.

According to an embodiment, said given performance criterion is anenergetic criterion, such as power or energy, and the third parameter isrepresentative of a time performance criterion, such as the operatingfrequency of the electronic circuit.

According to an embodiment, the target value is determined for theexecution of a task by the electronic circuit within a given timeperiod.

According to an embodiment, the method comprises, at step f), a firstoperation of the electronic circuit for a first time period by takingthe third parameter to said lower value, and a second operation of theelectronic circuit for a second time period by taking the thirdparameter to said upper value, the first and second operations beingalternately repeated.

According to an embodiment, the first parameter is the power supplyvoltage of the electronic circuit, the second parameter is the biasvoltage of metal-oxide field effect transistors of the electroniccircuit, and the third parameter is the clock frequency at which theelectronic circuit is rated.

Another embodiment provides a method of controlling a plurality ofelectronic circuits, comprising the steps of:

-   -   if the target value is located in one of the ranges of one of        the electronic circuits, having said electronic circuit operate        by taking the third parameter to the target value; and    -   in the opposite case, selecting the one of the electronic        circuits and, for said electronic circuit, selecting the two        ranges closest to the target value on either side thereof and        having said electronic circuit operate by successively taking        the third parameter into each of the two selected ranges.

According to an embodiment, the electronic circuit comprises at leasttwo electronic circuit sections, a rank being assigned to eachelectronic circuit section, and the first parameter is said rank.

Another embodiment provides an electronic circuit comprising:

-   -   actuators enabling to control the values of first, second, and        third parameters defining an operating configuration of the        electronic circuit, the first parameter being capable of taking        first discrete values, the second and third parameters being        capable of continuously or discretely varying;    -   a first unit comprising means for storing previously-obtained        information according to the above method and comprising, for        each value of the first parameter, an optimal variation range of        the third parameter associated with a corresponding range of        values of the second parameter, the optimal variation ranges all        being different, and comprising analysis means connected to the        storage means and enabling to associate a third value of the        third parameter to each pair of one of the first values of the        first parameter and of a second value of the second parameter;    -   a second unit capable of determining a target value of the third        parameter;    -   a third analysis unit capable of determining whether the target        value is located in one of the optimal variation ranges, and of        selecting this range in the case where it is and, in the        opposite case, of selecting the two ranges closest to the target        value on either side thereof, the analysis unit defining,        according to the case, one or two operating configurations with        a third parameter respectively having the target value or two        values respectively smaller and greater than said target value        and respectively contained in the two selected ranges, for each        configuration the first parameter taking a first value        corresponding to the range containing the value of the third        parameter and the second parameter taking the second value of        the pair associated with the third retained value; and    -   a fourth control unit capable of applying, via said actuators,        an operating configuration or as a variation, each of the two        operating configurations defined by the third analysis unit.

According to an embodiment, the first unit comprises means forimplementing the analysis method such as previously defined enabling todefine said information stored by said storage means.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features and advantages will be discussed indetail in the following non-limiting description of specific embodimentsin connection with the accompanying drawings, among which:

FIG. 1 partially and schematically shows an embodiment of an electroniccircuit;

FIG. 2 shows an example of maximum clock frequencies accessibleaccording to the power supply voltage and to the bulk bias voltage ofMOS transistors of the electronic circuit of FIG. 1;

FIG. 3 shows, in the form of a block diagram, an embodiment of a methodof determining minimum power operating configurations of the electroniccircuit of FIG. 1;

FIG. 4 shows an example of a curve of variation of the power consumed bythe electronic circuit of FIG. 1 according to the clock frequency duringvariations of the power supply voltage and of the bulk bias voltage ofMOS transistors of the electronic circuit;

FIG. 5 shows an example of a convex envelope of the variation curve ofFIG. 4;

FIG. 6 shows variation curves, according to the clock frequency, of thepower supply voltage and of the bulk bias voltage of MOS transistors ofthe electronic circuit of FIG. 1;

FIG. 7 shows, in the form of a block diagram, an embodiment of a methodof controlling the clock frequency, the power supply voltage, and thebulk bias voltage of MOS transistors of the electronic circuit of FIG.1;

FIG. 8 is a diagram similar to FIG. 5 and illustrates an embodiment ofthe embodiment of the control method of FIG. 7;

FIG. 9 is a diagram similar to FIG. 6 and illustrates another embodimentof the control method of FIG. 7;

FIG. 10 partially and schematically shows another embodiment of anelectronic circuit; and

FIG. 11 shows in the form of a block diagram an embodiment of a methodof controlling the electronic circuit of FIG. 10.

DETAILED DESCRIPTION

For clarity, the same elements have been designated with the samereference numerals in the various drawings and, further, the variousdrawings are not to scale. Further, in the following description, unlessotherwise indicated, terms “substantially”, “approximately”, and “in theorder of” mean “to within 10%”.

According to an embodiment, the control method comprises modifying threeoperating parameters of an electronic circuit enabling to achieve thedesired operating performances of the electronic circuit withsubstantially the lowest possible consumed power, where at least one ofthe operating parameters can only take discrete values while the otheroperating parameters may vary continuously or discretely with a finepitch, or discretely.

Preferably, at least one of the operating parameters of the electroniccircuit is representative of the operating speed of the electroniccircuit. It may be the clock frequency at which the electronic circuitis rated.

An embodiment will now be described in detail, where the three operatingparameters of the electronic circuit are the electronic circuit powersupply voltage, the clock frequency, and the bias voltage of bulks ofMOS transistors of the electronic circuit. As an example, in thisembodiment, the discretely-varying operating parameter is the powersupply voltage.

FIG. 1 shows an embodiment of an electronic circuit 10.

Electronic circuit 10 comprises a plurality of unit electronic circuits12, for example, from 1 to 64 circuits 12. Circuits 12 are capable ofoperating in parallel. Each unit electronic circuit 12 is connected to ageneral control unit 14 capable, in particular, of allocating the tasksto be performed to the different circuits 12. General control unit 14may be formed in centralized or distributed fashion in electroniccircuit 10. According to an embodiment, general control unit 14 maycomprise a processor capable of executing the instructions of a computerprogram stored in a memory. According to an example, general controlunit 14 may be formed by a dedicated circuit, for example, in the formof a state machine.

According to an embodiment, at least one of circuits 12 may be poweredat a power supply voltage V_(dd), which may be different from the powersupply voltages of the other unit electronic circuits 12. Preferably,each circuit 12 may be powered at a power supply voltage V_(dd), whichmay be different from the power supply voltages of the other unitelectronic circuits.

According to an embodiment, at least one of circuits 12 is a synchronouselectronic circuit or a locally synchronous electronic circuit, whichmay be rated by a clock frequency F which may be different from theclock frequencies rating the other unit electronic circuits 12.Preferably, each circuit 12 may be rated at a clock frequency F, whichmay be different from the clock frequencies rating the other unitelectronic circuits 12.

According to an embodiment, at least one of circuits 12 comprises MOStransistors and bulk bias voltage V_(bb) of the MOS transistors ofcircuit 12 may be modified. Preferably, all circuits 12 comprise MOStransistors and the bulk bias voltage of the MOS transistors of eachcircuit 12 may be different from the bias voltages of the other unitelectronic circuits 12.

The structure of one of unit electronic circuits 12 will now bedescribed. A plurality of unit electronic circuits 12 may have a similarstructure.

At least one of unit electronic circuits 12 comprises a processing unit20 capable, in particular, of performing calculations. It may be adedicated electronic circuit or a processor capable of executing theinstructions of a computer program stored in a memory. Processing unit20 is powered with power supply voltage V_(dd). The bulks of at leastsome MOS transistors of processing unit 20 are biased to bias voltageV_(bb). Processing unit 20 is rated at clock frequency F. Processingunit 20 is capable of executing the tasks assigned to circuit 12 bygeneral control unit 14.

Unit electronic circuit 12 comprises a local control unit 22 capable ofcontrolling at least three actuators 24, 26, 28. First actuator 24 iscapable of modifying frequency F. Second actuator 26 is capable ofmodifying power supply voltage V_(dd). According to an example, actuator26 may comprise a DC/DC converter controlled by unit 22. According toanother example, actuator 26 corresponds to a V_(dd) hopping circuit.Third actuator 28 is capable of modifying bias voltage V_(bb). Thirdactuator 28 may comprise a charge pump circuit.

Unit electronic circuit 12 may comprise sensors 30, for example,arranged in processing unit 20. One of sensors 30 may correspond to asensor providing a signal representative of temperature T in processingunit 20. One of sensors 30 may correspond to a sensor providing a signalrepresentative of temperature A in processing unit 20. Activity A ofcircuit 12 is for example an information representative of the number oflogic gates which switch within a defined time interval or the number oftransitions of the MOS transistors of processing unit 20 for the taskbeing executed. One of sensors 30 may correspond to a sensor providing asignal representative of power P consumed by processing unit 20.

Unit electronic circuit 12 may comprise an analysis unit 32 receivingthe signals provided by sensors 30. Analysis unit 32 is capable ofproviding data representative of operating configurations likely to beapplied by control unit 22. Such configurations are called optimalconfigurations hereafter. These are operating configurations of circuit12 where a parameter representative of the electric power consumption ofcircuit 12 is minimum or substantially minimum. This parameter forexample corresponds to the electric power consumed by circuit 12 or tothe electric energy used by circuit 12 for the execution of a task.

According to a variation, it is possible for temperature T not to bedirectly measured. Temperature T can then be determined by analysis unit32 based on signals provided by circuits 12 neighboring the consideredcircuit. According to a variation, it is possible not to directlymeasure activity A, which may be estimated by analysis unit 32.According to a variation, it is possible not to directly measureconsumed power P. Power P may then be estimated by analysis unit 32.Consumed power P may be estimated from the measurement of temperature T,of activity A, or power supply voltage V_(dd), and of bias voltageV_(bb). Consumed power P can be divided into a dynamic power P_(dyn) anda leakage power P_(leak). Dynamic power P_(dyn) is the consumed powerdue to the energy dissipated during state switchings of the logic gatesor during switchings between the on state and the off state of the MOStransistors. Leakage power P_(leak) is the consumed power due to thevarious losses of transistors other than dynamic power P_(dyn). Analysisunit 32 may determine an estimate of dynamic power P_(dyn) by amathematical function of frequency F, of activity A, and of power supplyvoltage V_(dd). Analysis unit 32 may determine an estimate of leakagepower P_(leak) by a mathematical function of frequency F, of powersupply voltage V_(dd), of temperature T, and of bias voltage V_(bb).

According to an embodiment, power supply voltage V_(dd) may take Ndiscrete values V_(dd,i), N being an integer for example varying from 2to 5 and i being an integer varying from 1 to N. Bias voltage V_(bb) mayvary continuously or discretely with a fine pitch, between a minimumvalue V_(bb,min,i) and a maximum value V_(bb,max,i), where the twovalues may depend on V_(dd,i).

Parameters V_(dd), V_(bb), and F depend on one another. Indeed, for agiven pair of voltages V_(dd) and V_(bb), there exists a maximum valueF_(max) of the clock frequency beyond which time errors may occur. Atime error for example occurs when the input signal of at least oneflip-flop is not established within a clock period. Generally, circuit12 is rated at maximum frequency F_(max), possibly by applying asecurity margin, which is allowed by the values of voltages V_(dd),V_(bb) applied to circuit 12.

In operation, electronic circuit 12 is led to perform a succession oftasks. A performance constraint is associated with the execution of eachtask. This means that the execution of the tasks should be over atlatest at the end of a determined time period. A possibility compriseshaving circuit 12 operate at a constant target clock frequencyF_(target), which is the clock frequency for which the execution of thetask is over at the end of the determined time period. Anotherpossibility is to have the circuit operate successively at differentclock frequencies so that the execution of the task is over at the endof the determined time period. The time performances of circuit 12 arethen equivalent to an operation at target clock frequency F_(target).Target clock frequencies F_(target) of successive tasks may vary fromone task to the other.

For each value of power supply voltage V_(dd,i), where i varies from 1to N, the maximum accessible clock frequency F_(max) at which theelectronic circuit can be rated varies within range [F_(max,i−),F_(max,i+)] when bias voltage V_(bb) varies from V_(bb,min,i) toV_(bb,max,i).

FIG. 2 shows an example of the maximum clock frequencies F_(max) whichmay be achieved for all possible pairs (V_(dd), V_(bb)) in the casewhere power supply voltage V_(dd) may take four values V_(dd1), V_(dd2),V_(dd3), or V_(dd4) and in the case where bias voltage V_(bb) may varyfrom V_(bb,min,i) to V_(bb,max,i), where i varies from 1 to 4. A singlepair of voltages (V_(dd), V_(bb)) corresponds to a point of one ofsegments A₁, A₂, A₃, or A₄.

Consider three target clock frequencies F_(target1), F_(target2), andF_(target3). As appears in FIG. 2, a single point B of one of segmentsA₁, A₂, A₃, and A₄ corresponds to target clock frequency F_(target1).This means that target clock frequency F_(target1) is only accessiblewith a single pair of voltages (V_(dd), V_(bb)). To decrease theelectric power consumption of circuit 12, it may be envisaged to applyvoltages V_(dd) and V_(bb) associated with point B and to rate thecircuit at target clock frequency F_(target1). However, this does notascertain that the power consumed by circuit 12 is minimum and thatthere exists no other solution for which the consumed power would belower for the same performance as that associated with point B.

Two points C and D of two different segments, A₃ and A₄, correspond totarget clock frequency F_(target2). Target clock frequency F_(target2)is thus accessible by two pairs of voltages (V_(dd), V_(bb)). A problemis to select the pair of voltages (V_(dd), V_(bb)) to be used. It ishowever not ascertained that the power consumed by the circuit isminimum for one or the other of these pairs of voltage.

No point of segments A₁, A₂, A₃, and A₄ corresponds to target clockfrequency F_(target3). A possibility would then be to rate the circuitat an accessible clock frequency higher than target clock frequencyF_(target3). However, the power consumed by the circuit then is notminimum. Another possibility would be to have circuit 12 successivelyoperate at a clock frequency F_(inf) lower than target clock frequencyF_(target3) and at a clock frequency F_(sup) higher than target clockfrequency F_(target3) or conversely. The problem then is to select thepairs of voltages (V_(dd), V_(bb)) to be used for frequencies F_(inf)and F_(sup) so that the consumed power is minimum.

According to an embodiment, a method of determining the operatingconfigurations of circuit 12 for which the power consumed by circuit 12is minimum, or substantially minimum, while reaching the desiredperformances, is implemented. Such operating configurations will becalled optimal configurations. Each optimal configuration corresponds toa triplet comprising a value of voltage V_(dd), a value of voltageV_(bb), and a corresponding maximum clock frequency value F_(max).

The method of determining the optimal configurations may be implementedon design of electronic circuit 10 or during a step of characterizationof electronic circuit 10 after manufacturing thereof. In this case, datarepresentative of the optimal configurations may be stored in a memoryof analysis unit 32. As a variation, the method of determining theoptimal configurations may be implemented by analysis unit 32 during theoperation of electronic circuit 10.

According to an embodiment, in operation, a control method comprisingselecting the optimal configuration or two optimal configurations to beapplied to achieve the desired performances and controlling theactuators to apply the selected optimal configuration or the selectedoptimal configurations is implemented.

FIG. 3 shows in the form of a block diagram an embodiment of the methodof determining the optimal configurations.

At step 40, for a determined temperature T and activity A, the set ofranges [F_(max,i−), F_(max,i+)] of maximum clock frequency F_(max,i),where i varies from 1 to N, likely to be obtained by varying powersupply voltage V_(dd) among values V_(dd,i) and by varying bias voltageV_(bb) between V_(bb,min,i) and V_(bb,max,i), is determined. SegmentsA₁, A₂, A₃, and A₄ previously described in relation with FIG. 2 show anexample of ranges [F_(max,i−), F_(max,i+)] of maximum clock frequenciesF_(max,i) in the case where N is equal to 4.

As an example, the determination of maximum clock frequency F_(max,i)obtained for a pair of voltages (V_(bb), V_(dd,i)) may be achieved viadelay sensors in the publication entitled “An innovative timing slackmonitor for variation tolerant circuits” of B. Rebaud et al. (IEEEInternational Conference on IC Design and Technology—ICICDT—2009, pages215-218, May 18-20, 2009).

The method carries on at step 42.

At step 42, power P consumed by processing unit 20 is determined foreach triplet (F_(max,i), V_(bb), V_(dd,i)) and for the determinedtemperature T and activity A. In the following description, calloperating point PM the power-clock frequency pair (P, F_(max,i)).

FIG. 4 shows an example of a curve C of variation of the consumed powerP according to clock frequency F, for a determined temperature T andactivity A, in the case where N is equal to 4. Each point of curve Ccorresponds to an operating point PM. Curve C comprises four arcs C₁,C₂, C₃, and C₄. Generally, curve C comprises N arcs C_(i), with ivarying from 1 to N, each arc C_(i) being obtained with power supplyvoltage V_(dd,i). For each arc C_(i), the point of the arc at frequencyF_(max,i−), that is, the left-hand end point in FIG. 4, is obtained forbias voltage V_(bb,min,i) and the point of the arc at frequencyF_(max,i+), that is, the right-hand end point in FIG. 4, is obtained forbias voltage V_(bb,max,i).

The method carries on at step 44.

At step 44, convex envelope C_(H) of curve C is determined. Convexenvelope C_(H) is defined, like curve C, for a determined temperature Tand activity A. Convex envelope C_(H) is defined by the followingrelations (1):

$\begin{matrix}{{C = {\bigcup_{i = {1\text{:}N}}C_{i}}}{{EF} = {\bigcup_{i = {1\text{:}N}}\lbrack {F_{\max,i} - F_{\max,i} +} \rbrack}}{a_{\in}\lbrack {0,1} \rbrack} = \begin{Bmatrix}{{( {P_{j,}F_{j}} ){{P( {{{aF}_{a}( {1 - a} )}F_{b}} )} \leq {{{aP}( F_{a} )} + {( {1 - a} ){P( F_{b} )}}}}},} \\{{F_{a} \neq F_{b}},{( {F_{a},F_{b}} ) \in {{EF} \times {EF}}}}\end{Bmatrix}} & (1)\end{matrix}$

This means that for two points PM_(a) and PM_(b) of convex envelopeC_(H), all the points of the arc of curve C_(H) between points PM_(a)and PM_(b) are located under the line connecting points PM_(a) andPM_(b). Convex envelope C_(H) comprises arcs C_(Hi), with i varying from1 to N, each arc C_(Hi) corresponding to a portion of arc C_(i).

It has been shown that if target clock frequency F_(target) correspondsto a frequency F_(max,i) associated with a point PM belonging to convexenvelope C_(H), the consumed power is then minimum. Further, it has beenshown that if target clock frequency F_(target) corresponds to afrequency F_(max,i) associated with a point PM which does not belong toconvex envelope C_(H), a minimum consumed power may be obtained byhaving processing unit 20 successively operate at a frequency F_(sup)greater than F_(target) and at a frequency F_(inf) smaller thanF_(target) or conversely, frequencies F_(sup) and F_(inf) being thefrequencies closest to F_(target) having points PM of convex envelopeC_(H) corresponding thereto.

The method carries on at step 46.

At step 46, the ends of each arc C_(Hi) of convex envelope C_(H) aredetermined.

FIG. 5 shows an example of a convex curve C_(H) associated with curve Cshown in FIG. 4. In FIG. 5, the portions of curve C which do not belongto curve C_(H) are shown in dotted lines. For each arc C_(Hi), a firstend point, noted PM_(i−), corresponds to the point of arc C_(Hi) forwhich bias voltage V_(bb) is the lowest, noted V_(bb,i−). The maximumfrequency of point PM_(i−) is noted F_(i−). The second end point, notedPM_(i+), corresponds to the point of arc C_(Hi) for which bias voltageV_(bb) is the highest, noted V_(bb,i+). The maximum frequencycorresponding to point PM_(i+) is noted F_(i+). The method carries on atstep 48.

At step 48, the values of triplets (V_(dd,i), V_(bb,i−), F_(i−)) and(V_(dd,i), V_(bb,i+), F_(i+)), for i varying from 1 to N, are stored ina memory of analysis unit 32. Further, data representative of the curvesof variation of bias voltage V_(bb,i) according to maximum clockfrequency F_(max) for each value V_(dd,i) of power supply voltage V_(dd)are stored in a memory of analysis unit 32. All these data correspond tothe data representative of the optimal configurations and are associatedwith a determined temperature T and activity A.

The data representative of the optimal configurations for a determinedtemperature T and activity A are indicated in table (1) hereafter:

TABLE (1) PM correspon- PM correspon- Power supply ding to the ding tothe Bias voltage V_(dd) lower limit upper limit voltage V_(bb) V_(dd, 1)V_(bb, 1) − (T, A), V_(bb, 1) + (T, A), V_(bb, 1)(^(F)max, F₁ − (T, A)F₁ + (T, A) T, A) V_(dd, 2) V_(bb, 2) − (T, A), V_(bb, 2) + (T, A),V_(bb, 2)(^(F)max, F₂ − (T, A) F₂ + (T, A) T, A) . . . . . . . . . . . .V_(dd, N) V_(bb, N) − (T, A), V_(bb, N) + (T, A), V_(bb, N)(^(F)max,F_(N) − (T, A) F_(N) + (T, A) T, A)

FIG. 6 shows the curves of variation, according to the clock frequency,of power supply voltage V_(dd) and of bias voltage V_(bb) for adetermined temperature T and activity A, obtained from the example ofconvex envelope of FIG. 5. These curves illustrate the datarepresentative of the optimal configurations.

According to an embodiment, previously-described steps 40 to 48 arerepeated a plurality of times for a plurality of values of temperature Tand/or a plurality of values of activity A. For each value oftemperature T and/or of activity A, the data representative of theoptimal configurations are stored in the memory of analysis unit 32.

According to another embodiment, previously-described steps 40 to 48 arecarried out by analysis unit 32 in operation. Analysis unit 32determines points PM based on values of temperature T and activity Adetermined from the signals provided by sensors 30. In the case of avariation of temperature T or of activity A, analysis unit 32 maydetermine new values of points PM. As an example, it is possible to onlydetermine new values of points PM when temperature T varies beyond athreshold or when activity A varies beyond a threshold.

The determination of convex envelope C_(H), at previously-described step42, requires measuring the power consumed by processing unit 20.However, such a measurement may be difficult to perform. According to anembodiment, the determination of frequency ranges [F_(i−),F_(i+)], withi varying from 1 to N, is performed from the frequency ranges[F_(max,i−),F_(max,i+)] determined at step 40. As an example, range[F_(i−),F_(i+)] is equal to range [F_(max,i−),F_(max,i+)] at which theportions common (possibly with added margins) with another range[F_(max,j−),F_(max,j+)], where j is an integer different from i, areremoved. However, the power consumed over such frequency ranges maypossibly not be minimum.

It should be noted that in this simplified embodiment, frequency ranges[F_(i−),F_(i+)] which are relatively close to those obtained byimplementing the entire previously-described method are obtained.

In the previously-described embodiment, the optimal configurationscorrespond to the configurations for which the power consumed byelectronic circuit 12 is minimum. As a variation, instead of using theelectric power consumed by processing unit 20, it is possible toconsider the electric energy used to carry out the considered task. Theoptimal configurations then are those for which the energy used isminimum.

In the previously-described embodiment, curve C of variation of theconsumed power according to the clock frequency of circuit 12 has beenused and convex envelope C_(H) of curve C has been determined. It shouldhowever be clear that the curve of variation of the inverse of theconsumed power (or of the inverse of the energy used) may be used. Inthis case, the concave envelope of the curve of variation of the inverseof the consumed power is used.

FIG. 7 shows, in the form of a block diagram, an embodiment of themethod of controlling power supply voltage V_(dd), bias voltage V_(bb),and clock frequency F of circuit 12.

General control unit 14 provides local control unit 22 of circuit 12with a signal representative of target clock frequency F_(target) forthe task to be executed by circuit 12.

At step 50, analysis unit 32 determines whether target clock frequencyF_(target) is between frequencies F_(i−) and F_(i+), for i varying from1 to N, stored in the memory.

According to an embodiment, data representative of the optimalconfigurations have been determined and stored in analysis unit 32 for aplurality of temperature values T and a plurality of activity values A.

In the case where analysis circuit 32 is capable of determining, fromdirect measurements or by estimation, temperature T and activity A ofprocessing unit 20, analysis unit 32 may select frequency values F_(i−)and F_(i+), for i varying from 1 to N, of the data representative of theoptimal configurations which have been determined at the temperatureclosest to the measured/estimated temperature and at the activityclosest to the measured/estimated activity. As a variation, analysisunit 32 may determine new data representative of optimal configurations,and thus new values of frequencies F_(i−) and F_(i+), for i varying from1 to N, by interpolation at the measured/estimated temperature T and atthe measured/estimated activity A based on data representative of theoptimal configurations which have been determined at the closesttemperatures T on either side of the measured/estimated temperature andat the closest activities A on either side of the closest activity.

According to an embodiment, data representative of the optimalconfigurations have been determined and stored in analysis unit 32 for asingle value of temperature T and a single value of activity A. Analysisunit 32 can thus select frequency values F_(i−) and F_(i+), for ivarying from 1 to N, stored in the memory of analysis unit 32. As avariation, analysis unit 32 may determined new data representative ofoptimal configurations, and thus new values of frequencies F_(i−) andF_(i+), for i varying from 1 to N, by interpolation at themeasured/estimated temperature T and at the measured/estimated activityA based on data representative of the configurations stored in thememory of analysis unit 32.

It should be noted that whatever the retained storage form, more or lessdetailed, the number of stored data remains small. Such a simplicity isobtained due to the presentation of the information in a limited numberof segments, corresponding to a limited number of discrete values of thefirst parameter (Vdd). Further, the analysis of the variation curveobtained for different sets of discrete values of the first parametermay be an element for aiding the selection of discrete values of thisfirst parameter.

If, at step 50, target clock frequency F_(target) is in one of ranges[F_(i−), F_(i+)], for i varying from 1 to N, determined by analysis unit32, then the method carries on to step 52 where a first control mode,called Mode 1, is implemented. If, at step 50, target clock frequencyF_(target) is not in one of ranges [F_(i−), F_(i+)], for i varying from1 to N, determined by analysis unit 32, then the method carries on tostep 54 where a second control mode, called Mode 2, is implemented.

FIG. 8 is a diagram similar to FIG. 5 which further shows the frequencyranges where the first control mode, Mode 1, is implemented and thefrequency ranges where the second control mode, Mode 2, is implemented.

At step 52, analysis unit 32 determines the value of bias voltage V_(bb)for which the target clock frequency is obtained based on the datarepresentative of the optimal configurations determined by analysis unit32. Since point PM at target clock frequency F_(target) belongs toconvex envelope C_(H), the consumed power is minimum. Unit 22 controlsactuator 24 to take the clock frequency to target clock frequencyF_(target). Unit 22 further controls actuator 26 to take power supplyvoltage V_(dd) to power supply voltage V_(dd,i) and unit 22 controlsactuator 28 to take bias voltage V_(bb) to the determined value. Themodifications of the clock frequency, of power supply voltage V_(dd),and of bias voltage V_(bb) are performed to guarantee that there will beno time errors.

At step 54, analysis unit 32 determines at least two clock frequenciesF_(inf) and F_(sup) corresponding to points PM belonging to complexenvelope C_(H), clock frequency F_(inf) being smaller than target clockfrequency F_(target) and clock frequency F_(sup) being greater thantarget clock frequency F_(target). According to an embodiment, theselected points PM are the end points of the two arcs of the convexenvelope having associated clock frequencies closest to target clockfrequency F_(target).

Unit 22 controls actuator 24 to successively take the clock frequency tovalue F_(sup) for a time period D_(sup) and to value F_(inf) for a timeperiod D_(inf) As a variation, clock frequency F_(sup) may be appliedafter clock frequency F_(inf) As an example, calling D_(t) the timetaken to execute the task at target clock frequency F_(target), timeperiods D_(inf) and D_(sup) may be determined according to the followingrelations (2):

Dsup=αDt

Dinf=(1−α)Dt

α=(Ftarget−Finf)/(Fsup−Finf)  (2)

FIG. 8 illustrates an example in the case where target clock frequencyF_(target) is located between the abscissas of points PM₁₊ and PM²⁻respectively corresponding to triplets (V_(dd,1), V_(bb,1+), F₁₊) and(V_(dd,2), V_(bb,2−), F²⁻).

In this case, the power consumed during the successive application ofthe values of triplet (V_(dd,1), V_(bb,1+), F₁₊) and of the values oftriplet (V_(dd,2), V_(bb,2−), F²⁻) is minimum. In FIG. 8, this powercorresponds to the point at frequency F_(target) belonging to line Lshown in dotted lines connecting points PM₁₊ and PM²⁻.

The embodiment previously described in relation with FIG. 8 implies asimultaneous modification of the clock frequency, of power supplyvoltage V_(dd), and of bias voltage V_(bb). However, according to thetype of actuators 22, 24, and 26 used, the passing from a first value toa second value of clock frequency F_(max), of power supply voltageV_(dd), and/or of bias voltage V_(bb) may require a non-negligibletransition time.

According to an embodiment, it may be passed from point PM_(sup) topoint PM_(inf) via an intermediary point PM_(int). Point PM_(int) isassociated with a triplet (V_(dd), V_(bb), F_(max)) having a componentidentical to the triplet associated with point PM_(inf) and a componentidentical to the triplet associated with point PM_(sup). The thirdcomponent is selected to guarantee that the circuit is functional.Thereby, on passing from point PM_(sup) to point PM_(int), only twoparameters are modified. The passing from point P_(Mint) to pointPM_(inf) is then obtained by varying the value of the unmodifiedparameter from the value for point PM_(sup) to the value for pointPM_(inf), the third parameter being modified to the value associatedwith point PM_(inf).

FIG. 9 is similar to FIG. 6 and illustrates such an embodiment in thecase where bias voltage V_(bb) is the parameter for which the transitionbetween two values is not instantaneous. Unit 20 controls actuators 22,24, and 26 to point PM_(sup) associated with triplet (V_(dd,2),V_(bb,2−), F²⁻) for a time period α′D_(t). Unit 20 then controlsactuators 22 and 24 to point PM_(int) associated with triplet (V_(dd,1),V_(bb,2−), F_(int)). Unit 20 then controls actuators 22 and 26 to pass,within a time γ′D_(t), from point PM_(int) to point PM_(inf) by varyingthe bias voltage from V_(bb,2−) to V_(bb,1+) and by varying thefrequency from F_(int) to F₁₊. Time period γ′ depends on the dynamicrange of actuator 26. Circuit 12 is maintained at point PM_(inf) for atime period β′D_(t).

FIG. 10 shows another embodiment of an electronic circuit 60. Electroniccircuit 60 comprises all the elements of electronic circuit 10 shown inFIG. 1. Electronic circuit 60 further comprises an interconnectionnetwork 62 capable of allowing a data exchange between unit electroniccircuits 12. Interconnection network 62 may comprise a data exchange busor correspond to a network-on-chip. The electronic circuit comprises Kelementary electronic circuits 12, K being an integer greater than 1. Asan example, in FIG. 10, K is equal to four.

General control unit 14 is capable of allocating the tasks to beexecuted to the different unit electronic circuits 12. An applicationcomprising M tasks Task_(m) to be assigned is considered, M being aninteger greater than 1 and m being an integer which varies from 1 to M.Each task Task_(m) has an associated target clock signal F_(target,m)for the execution of this task. The target clock frequencies may bedetermined by general control unit 14.

General control unit 14 is capable of collecting the data representativeof the optimal configurations of each circuit 12. The datarepresentative of the optimal configurations have been determined byeach electronic circuit 12 as previously described.

In the case where one of circuits 12 updates its data representative ofoptimal configurations, the updated data are transmitted to unit 14.

FIG. 11 shows, in the form of a block diagram, an embodiment of themethod of task assignment by general control unit 14. The method isimplemented for each task Task_(m) to be executed.

At step 70, general control unit 14 determines whether target clockfrequency F_(target,m) of task Task_(m) is contained in one of theaccessible frequency ranges [F_(i−),F_(i+)] of one of electroniccircuits 12. If target clock frequency F_(target,m) is contained in oneof the accessible frequency ranges [F_(i−),F_(i+)] of one of electroniccircuits 12, unit 14 selects this circuit 12 if the latter is notalready executing a task and the method carries on to step 72. If targetclock frequency F_(target,m) is not contained in one of the accessiblefrequency ranges [F_(i−), F_(i+)] of one of electronic circuits 12,general control unit 14 selects the available electronic circuit 12 forwhich the consumed power is the lowest by applying previously-describedcontrol mode Mode 2 and the method carries on to step 74.

At step 72, unit 14 assigns task Task_(m) to the selected electroniccircuit 12 and transmits target clock frequency F_(target,m) to theselected electronic circuit 12. The selected circuit 12 then implementsa control method of Mode 1 type such as previously described.

At step 74, unit 14 assigns task Task_(m) to the selected electroniccircuit 12 and transmits target clock frequency F_(target,m) to theselected electronic circuit 12. The selected circuit 12 then implementsa control method of Mode 2 type such as previously described.

Specific embodiments have been described. Various alterations andmodifications will occur to those skilled in the art. Although, in thepreviously described embodiments, the used operating parameters of theelectronic circuit are the clock frequency, the power supply voltage,and the transistor bulk bias voltage, other operating parameters may beused. As an example, a parameter representative of the operating speedof the electronic circuit, other than the clock frequency, may be used.In particular, in the case of an electronic circuit implementing a harddisk data storage system, the rotation speed of the hard disk may beused as an operating parameter.

Although embodiments where the discrete operating parameter is theelectronic circuit power supply voltage have been described, anotherdiscrete operating parameter may be used. Indeed, considering theelectronic circuit 60 shown in FIG. 10, the rank, or number, of circuit12 to which the task is assigned may be the discrete operating parameterof circuit 60. An actuator of such an operating parameter is thencapable of having a circuit 12 execute a task initially executed byanother circuit 12. The use of the rank as an operating parameter isparticularly advantageous in the case where circuits 12 have differentperformances, for example, in terms of power consumption and operatingspeed. The two other following continuously-varying operating parametersmay further be used: the clock frequency of each circuit 12 and the bulkbias voltage of MOS transistors of each circuit 12 or the power supplyvoltage of each circuit 12 in the case of a power supply voltage varyingcontinuously, or discretely with a fine pitch, or discretely.

Further, the target operating parameter may be a voltage, for example,the power supply voltage delivered by a battery. In this case, it couldbe desired to adapt the operating parameters, for example, the operatingfrequency, to optimize a performance criterion, such as the circuitpower consumption. In this case, one may have, as first, second, andthird operating parameters, respectively, bulk bias voltage V_(bb), thecircuit frequency, and the circuit power supply voltage. There wouldthen be variation ranges of minimum power supply voltage according tofrequency for a given bias voltage value.

Further, it could be desired to optimize a performance criterion otherthan an energetic performance criterion (power, energy . . . ), forexample a circuit temperature, heating, or aging criterion.

Further, in the previously-described embodiments, envelope C_(H) of thedata representative of the performance criterion is always increasing(for example, for the power according to the maximum frequency, shown inFIG. 4) or always decreasing (taking, for example, the energy accordingto the clock period). In the case where an increasing and thendecreasing envelope, or conversely, according to the third parameter,would be obtained, it is most likely that one part of the configurationsassociated with the decreasing or increasing portion is sub-optimal ascompared with the other part. In this case, an only increasing or onlydecreasing portion of the envelope will be kept in practice. As anexample, considering that the third parameter is the clock period of thecircuit (1/frequency) and that the variation curve is the energy versusthe period, it is then highly possible for the convex envelope to beeither decreasing, or increasing. In this case, it can be observed thatthe static power consumption becomes preponderating over the dynamicpower consumption when the period becomes too long (the frequencybecomes too small) and it will be more judicious to operate the circuitat relatively low frequencies, corresponding to the decreasing portionof the envelope (with the optional possibility of setting the circuit tostandby if the execution of the tasks has ended faster than requested).

Further, it will readily occur to those skilled in the art that therange of useful values of the third parameter will be limited andbetween minimum and maximum values of the third parameter capable ofcorresponding to the retained configurations so that the analysis methoddevelops properly.

1. A method of analyzing an electronic circuit (12) enabling todetermine optimal operating configurations of the electronic circuitaccording to a given performance criterion, each operating configurationof the electronic circuit being defined by values taken by first,second, and third operating parameters, the first parameter beingcapable of taking first discrete values, the second and third parametersbeing capable of continuously or discretely varying, the secondparameter being capable of varying between a minimum value and a maximumvalue, each pair of a first value of the first parameter and of a secondvalue of the second parameter having an associated third limiting valueof the third parameter beyond which the circuit may no longer operate,the method comprising the steps of: a) determining, for each value ofthe first parameter, a limiting variation range of the third parameterby varying the second parameter between the minimum and maximum valuesof this second parameter and by searching the third correspondinglimiting values of the third parameter; and b) determining, for eachvalue of the first parameter, an optimal variation range of the thirdparameter corresponding to all or part of said limiting variation rangeof the third parameter previously determined for the value of the firstconsidered parameter, so that the optimal variation ranges selected forthe different values of the first parameter are all different.
 2. Themethod of claim 1, further comprising an additional step c) betweensteps a) and b), step c) comprising determining a curve of variation ofdata representative of said performance criterion according to the thirdparameter, by defining, for each first value of the first parameter, anarc of a curve corresponding to the values of said representative dataobtained over the limiting variation range of the third parameterassociated with the first considered parameter and the correspondingvariation range of the second parameter and wherein, at step b), foreach value of the first parameter, an optimal variation range of thethird parameter corresponding to all or part of said limiting variationrange of the third parameter previously determined for the value of thefirst considered parameter is determined, so that the optimal variationranges selected for the different values of the first parameter are alldifferent and so that the portions of arc of a curve associated with theselected optimal variation ranges meet at best the performance criterionof the electronic circuit for the corresponding values of the thirdparameter.
 3. The method of claim 2, wherein step c) comprises the stepsof: determining the convex or concave envelope of said variation curve;and searching for the portions of said limiting variation ranges of thethird parameter which correspond to said envelope and retaining theseportions as optimal variation ranges.
 4. A method of controlling anelectronic circuit enabling to determine an optimal operatingconfiguration of the electronic circuit according to a given performancecriterion, each operating configuration of the electronic circuit beingdefined by given values of first, second, and third operatingparameters, the first parameter being capable of taking first discretevalues, the second and third parameters being capable of continuously ordiscretely varying, the electronic circuit comprising means for storinginformation previously obtained by the method of claim 1 and comprising,for each value of the first parameter, an optimal variation range of thethird parameter associated with a corresponding range of values of thesecond parameter, the optimal variation ranges all being different, theelectronic circuit comprising analysis means enabling, for each pair ofone of the first values of the first parameter and of a second value ofthe second parameter, to associate therewith a third value of the thirdparameter, the method comprising the steps of: d) determining a targetvalue of the third parameter; e) if the target value is located in oneof the optimal variation ranges of the third parameter, selecting thisoptimal variation range and having the electronic circuit operate bytaking the third parameter to the target value; and f) in the oppositecase, selecting the two ranges of optimal values of the third parameterclosest to the target value on either side thereof and having theelectronic circuit operate by successively taking the third parameterinto each of the two selected optimal variation ranges, between a lowervalue and an upper value of the third parameter on each side of thetarget value; and wherein, at steps e) or f), the first parameter istaken to the first value corresponding to the range containing the thirdapplied value and the second parameter is taken to the second value ofthe pair associated with the third applied value.
 5. The method of claim1, wherein said given performance criterion is an energetic criterion,and the third parameter is representative of a time performancecriterion.
 6. The method of claim 4, wherein the target value isdetermined for the execution of a task by the electronic circuit withina given time.
 7. The method of claim 4, comprising, at step f), a firstoperation of the electronic circuit for a first time period by takingthe third parameter to said lower value, and a second operation of theelectronic circuit for a second time period by taking the thirdparameter to said upper value, the first and second operations beingalternately repeated.
 8. The method of claim 1, wherein the firstparameter is the power supply voltage of the electronic circuit, thesecond parameter is the bias voltage of metal-oxide field effecttransistors of the electronic circuit, and the third parameter is theclock frequency at which the electronic circuit is rated.
 9. The methodof claim 3, for controlling a plurality of electronic circuits,comprising the steps of: if the target value is located in one of theranges of one of the electronic circuits, having said electronic circuitoperate by taking the third parameter to the target value; and in theopposite case, selecting one of the electronic circuits and, for saidelectronic circuit, selecting the two ranges closest to the target valueon either side thereof and having said electronic circuit operate bysuccessively taking the third parameter into each of the two selectedranges.
 10. The method of claim 1, wherein the electronic circuitcomprises at least two electronic circuit sections, a rank beingassigned to each electronic circuit section, and wherein the firstparameter is said rank.
 11. An electronic circuit comprising: actuatorsenabling to control the values of first, second, and third parametersdefining an operating configuration of the electronic circuit, the firstparameter being capable of taking first discrete values, the second andthird parameters being capable of continuously or discretely varying; afirst unit comprising means for storing information previously obtainedaccording to the method of claim 1 and comprising, for each value of thefirst parameter, an optimal variation range of the third parameterassociated with a corresponding range of values of the second parameter,the optimal variation ranges all being different, and comprisinganalysis means connected to the storage means and enabling to associatea third value of the third parameter to each pair of one of the firstvalues of the first parameter and of a second value of the secondparameter; a second unit capable of determining a target value of thethird parameter; a third analysis unit capable of determining whetherthe target value is located in one of the optimal variation ranges, andof selecting this range in the case where it is and, in the oppositecase, of selecting the two ranges closest to the target value on eitherside thereof, the analysis unit defining according to the case one ortwo operating configurations with a third parameter respectively havingthe target value or two values respectively smaller and greater thansaid target value and respectively belonging to the two selected ranges,for each configuration the first parameter taking a first valuecorresponding to the range containing the value of the third parameterand the second parameter taking the second value of the pair associatedwith the third selected value; and a fourth control unit capable ofapplying, via said actuators, an operating configuration or, as avariation, each of the two operating configurations defined by the thirdanalysis unit.
 12. (canceled)
 13. An electronic circuit comprising:actuators enabling to control the values of first, second, and thirdparameters defining an operating configuration of the electroniccircuit, the first parameter being capable of taking first discretevalues, the second and third parameters being capable of continuously ordiscretely varying; a first unit comprising means for storinginformation previously obtained according to the method of claim 1 andcomprising, for each value of the first parameter, an optimal variationrange of the third parameter associated with a corresponding range ofvalues of the second parameter, the optimal variation ranges all beingdifferent, and comprising analysis means connected to the storage meansand enabling to associate a third value of the third parameter to eachpair of one of the first values of the first parameter and of a secondvalue of the second parameter; a second unit capable of determining atarget value of the third parameter; a third analysis unit capable ofdetermining whether the target value is located in one of the optimalvariation ranges, and of selecting this range in the case where it isand, in the opposite case, of selecting the two ranges closest to thetarget value on either side thereof, the analysis unit definingaccording to the case one or two operating configurations with a thirdparameter respectively having the target value or two valuesrespectively smaller and greater than said target value and respectivelybelonging to the two selected ranges, for each configuration the firstparameter taking a first value corresponding to the range containing thevalue of the third parameter and the second parameter taking the secondvalue of the pair associated with the third selected value; and a fourthcontrol unit capable of applying, via said actuators, an operatingconfiguration or, as a variation, each of the two operatingconfigurations defined by the third analysis unit, wherein the firstunit comprises means for implementing the analysis method of claim 1enabling to define said information stored by said storage means.
 14. Anelectronic circuit comprising: actuators enabling to control the valuesof first, second, and third parameters defining an operatingconfiguration of the electronic circuit, the first parameter beingcapable of taking first discrete values, the second and third parametersbeing capable of continuously or discretely varying; a first unitcomprising means for storing information previously obtained accordingto the method of claim 2 and comprising, for each value of the firstparameter, an optimal variation range of the third parameter associatedwith a corresponding range of values of the second parameter, theoptimal variation ranges all being different, and comprising analysismeans connected to the storage means and enabling to associate a thirdvalue of the third parameter to each pair of one of the first values ofthe first parameter and of a second value of the second parameter; asecond unit capable of determining a target value of the thirdparameter; a third analysis unit capable of determining whether thetarget value is located in one of the optimal variation ranges, and ofselecting this range in the case where it is and, in the opposite case,of selecting the two ranges closest to the target value on either sidethereof, the analysis unit defining according to the case one or twooperating configurations with a third parameter respectively having thetarget value or two values respectively smaller and greater than saidtarget value and respectively belonging to the two selected ranges, foreach configuration the first parameter taking a first valuecorresponding to the range containing the value of the third parameterand the second parameter taking the second value of the pair associatedwith the third selected value; and a fourth control unit capable ofapplying, via said actuators, an operating configuration or, as avariation, each of the two operating configurations defined by the thirdanalysis unit, wherein the first unit comprises means for implementingthe analysis method of claim 2 enabling to define said informationstored by said storage means.